Conventional techniques for precision machining of metal surfaces require that a workpiece be subjected to a conventional machining operation in a first machine and than be transferred to a second machine for a precision grinding and polishing operation. The required use of at least two processing machines involving the transfer of the workpiece from one to the other adds significantly to the time and cost involved in precision surface finishing and limits the quality which can be achieved. It is therefore desired to provide apparatus which is capable of producing a precision finished surface while requiring the use of only a single machine tool having replaceable polishing elements.
There are known tool heads comprising freely rotating cup cutters. Examples of such devices are shown in USSR Pat. Nos. 261873 and 272791 of 1970. There are also known tool heads for use in association with a metal lathe and comprising freely rotating round cutters. These are illustrated in "Progressive Methods of Rotating Cutting of Metals" Minsk 1972, USSR. None of the known devices described above is capable of producing surface smoothness in the desired range of between 2 and 4 microinch r.m.s.
The present invention seeks to overcome disadvantages of the known prior art devices described above and provides tool heads for use in machine tools for producing high precision finishes in the range of 2-4 microinch r.m.s. or higher.
There are also known cutting tools which are provided with freely rotatable finishing heads. One example of such a tool is shown in U.S. Pat. No. 2,885,766 (Ernst et al.) which describes a face milling cutter including cutting rollers having finishing grooves as well as other grooved cutting rollers all of which are freely rotatable on a base and arranged for rotation in one direction on the spindle of a milling tool. Such tools are designed for fine cutting of metal surfaces and produce a finish no better than 32 microinch r.m.s. They are entirely distinct from polishing tools which are capable of producing a much finer quality surface finish.
Various types of finishing rollers are known and presently in use. U.S. Pat. No. 2,259,685 shows a finishing roller which comprises a resilient core surrounded by a rigid metal plate on the outside surface of which is disposed a thin layer of abrasive material. U.S. Pat. No. 2,024,591 describes an abrasive wheel comprising a resilient inner portion coated with a relatively thin abrasive layer.